Phosphoric acid (H3PO4) for use in fertilizer production is typically produced by a wet-process during which naturally occurring phosphate rock is reacted with sulphuric acid to provide so called wet-process phosphoric acid (WPA). Depending on the source of the phosphate rock, it may contain valuable metals such as uranium, vanadium and yttrium, which are dissolved by the sulphuric acid and form impurity constituents of the WPA.
In the United States, plants have been in operation since the early 1950's to recover valuable amounts of uranium from WPA. However, with fluctuations in the spot price of uranium it is important that it can be extracted from the WPA in a cost-effective manner. To date, many of the plants that have operated uranium extraction processes have utilized solvent extraction process to extract the uranium from the WPA. Another process that has received greater attention in recent times is an ion exchange process whereby WPA containing uranium is loaded onto an ion exchange resin. The WPA is flushed from the resin, leaving the uranium bound to the resin. The uranium is then eluted from the resin. U.S. Pat. No. 4,599,221 (Ketzinel et al.) discloses such a process for extracting uranium from WPA using an ion exchange process.
Unfortunately, the known uranium extraction processes are not all that simple to carry out. Part of the problem is that the WPA is a crude material containing a range of organic and inorganic contaminants or species that can interfere with the extraction process and have a profound effect on the commercial viability of the process.
The applicant has previously discovered that certain process efficiencies are achieved by lowering the iron concentration of the WPA, reducing the valency of any remaining ferric iron in the WPA to ferrous iron, and then extracting uranium compounds from the WPA. These details are disclosed in U.S. Pat. No. 8,226,910, which is incorporated by reference in its entirety.
There remains a need for other improved processes for extracting uranium from WPA that overcome one or more of the problems associated with others' processes and/or that are more efficient.